At typical flight altitudes of commercial or transport aircraft, pressure and temperature are lower than acceptable for a cabin region. Pressure-controlled cabins with global air conditioning systems belong to the prior art. By restricting the air conditioning of the cabin region to temperature adjustment, the air humidity during the flight can fall to very low values of a few per cent relative air humidity, for example 3-5%. The comfort of persons on board who spend quite a long time in this dry atmospheric environment is considerably reduced, since the low air humidity is felt to be unpleasant.
Besides the temperature control, known global air conditioning systems allow a humidification of the entire cabin air, so that a relative air humidity of, for example, 30-50% is established. As a result, a more pleasant atmospheric environment can be produced and thus the comfort on board increased.
An appropriate solution is described in the patent U.S. Pat. No. 5,595,690. There, membrane sheets are proposed for the central humidification. Since the required exchange area for a centralised solution is correspondingly large, the flat, extended design has proved to be disadvantageous on integration in the aircraft. Furthermore, a humidification of the entire cabin air involves increased energy expenditure and water tanks of corresponding size, and thus the proposed solution results in increased flying weight and fuel consumption of the aircraft. In addition, the membrane modules dry after the system is switched off, and the contraction of the membrane as it dries out causes considerable mechanical stresses on the membrane module frame. Depending on the type of connection and seal between adjacent sheets of the sheet membrane module, deformations due to the mechanical stress can cause leakage of the module.
A further disadvantage of a global or centralised humidification of the cabin air is the danger of undesired condensation, in particular in the vicinity of structural parts of the aircraft which are relatively cold in flight. Corrosion, malfunctions, weight increase due to water stored in the insulation or reduction of insulating properties may result from the formation of the condensate.
Solutions for local humidification are also known, for example, from laid-open application DE 10 2004 024 615 A1. There, spraying methods are used for local humidification. As a result, the air humidity can be increased in a targeted manner in partial regions of the cabin, without causing condensation on more remote, cooler insulation and structural parts of the aircraft. The disadvantage, however, is that owing to the spraying method the water supplied to an air stream to be humidified is supplied at least largely in liquid form. As a result, air containing a large number of small liquid drops, i.e. aerosols, is expelled into the cabin. The liquid drops entering the cabin region are generally felt by the cabin occupants to have an adverse effect on comfort. Furthermore, the danger of transmitting germs in breathing air increases due to the aerosols.
An object of the present invention is to ensure a high degree of climatic comfort for is persons on board, while maintaining efficient and safe flying operation.